Exposure Guide

Glad you could make it back! Here’s the exposure guide I promised. It’s not the last word on exposure by a long shot, but it’ll get most people going right off the bat with reasonable exposures.

There are other ways to gage exposure, I like this one. But then again I’ve always liked flying by the seat of my pants…

The ‘Seat-O-the-Pants’ Guide to pinhole exposures

First a little bit about the size of your pinhole relative to the size of your camera. I usually go with the rule of thumb that says that is your camera has a focal length of 6″ then your pinhole should be .5mm in diameter. This is a rough measure, but it gets you into the right area. The table below explains the other rules of thumb that you might want to try.

When you make the pinhole use a ‘drilling’ motion to get the pin through the tin or brass sheet. This avoids making a big, messy, rough hole…(not that every pinhole has to be perfect) but until you get the hang of making cameras it might be a good idea to make things as “normal” (what ever that is) as possible.

I use aluminum baking sheets from the grocery store for my pinhole material. It’s cheaper and just as good as brass…up to you really.

ATTENTION!…ok, now that I’ve got your attention…Larry Fratkin has created a really useful tool for calculating the focal length and pinhole diameter of your camera…try it! And once you try it let Larry know what you think of it!

Camera Length

Needle Size

Diameter
of hole

Relative
f/stop

8″

8

.023″

f/350

6.5″

9

.020″

f/300

5″

10

.018″

f/280

4″

12

.016

f/250

2.5″

13

.013

f/190

or you could use this formula…
dia/focal length

or…

the optimum pinhole = the sq.root of 0.0016
multiplied by the pinhole to film distance…

Open Shade or heavily overcast
No shadows
Either a grey day or
in the shadow of a tall building

250
300
350

14 minutes
23 minutes
36 minutes

47 seconds
1.3 minutes
2.0 minutes

9.2 seconds
15 seconds
24 seconds

Dawn or Dusk
Dark out here…
Like it says. Early morning
or early evening

250
300
350

38 minutes
1 hour
1.6 hours

2.1 minutes
3.5 minutes
5.4 minutes

25 seconds
42 seconds
1 minute

Ok. Keep in mind that all these times are just starting points. As you make more exposures and get better at making guesses that work you’ll make your own exposure chart.

When you make an exposure that is just way too dark as a print then double the exposure you gave the neg. If your print is just too light then halve the exposure. It might sound like the long way around but by splitting the differences each time you can arrive at a pretty good exposure in a your first few attempts.

Another great idea is to keep a notebook of all your exposures, the weather conditions, the film or paper etc.